The proposed research has four aims: 1) to further explore the meaning and accuracy of a recently proposed measure of household complexity, (the index of overall headship), and to test possible refinements; 2) to compute the index for as many nations, past and present, as have the needed data; 3) to study the social, cultural, economic and demographic correlates of household structure by means of cross-sectional comparisons among and within national populations, and by means of time-series analyses for selected nations; 4) to integret the empirical results in the light of literature on comparative household/family structure. The proposed research will involve a detailed critical analysis of existing census materials, supplemented by other existing data on demographic and socio-economic variables. Within the limits of existing data and methodologies, the research should yield data on household structure for a much larger and more representive sample of populations than ever before. The research would have broad significance since household structure and change have recently been cited as key variables in fertility transitions and as important determinants of individual economic well-being. The research also will have relevance to contemporary problems associated with the increasing residential isolation of the elderly in advanced nations such as U.S., the residential arrangements of young, unmarried adults, and the growth of one-parent families.